1. Field of the Invention
The present invention relates to a control method of an engine with direct fuel injection into the cylinder (so-called a direct injection engine) and more particularly to a control method of an injector which injects fuel into the cylinder. The invention is also related to a controller for implementing the control method or a control circuit device used for the controller.
2. Description of the Related Art
When an engine is started up in a cold state, a catalyst provided in an exhaust gas passage cannot be activated sufficiently because of the low temperature thereof. Accordingly, unburnt gas is discharged from the engine as it is, which will significantly affect the environment.
To reduce the amount of unburnt hydrocarbon (HC) discharged immediately after a cold start of an engine, it is conventionally proposed that fuel injection is performed at a later stage of the compression stroke and ignition performed after the T.D.C. This allows the air-fuel mixture in the cylinder to combust in a middle or later stage of the expansion stroke. As a result, the exhaust gas temperature rises activating the catalyst at an early stage. In the case of heavy fuels, the degradation of combustion stability is restrained by correcting an advance angle for the fuel injection timing and ignition timing at a later stage of the compression stroke. Further, a technique for changing the fuel injection timing according to fuel evaporation characteristics in a direct injection engine is disclosed, for example, in JP-A-2006-90202.